Patent GB-667370-A (GB)
Title: Improvements in or relating to electrical selecting systems and more especially to automatic telephone exchange systems
Inventor: FLOWERS THOMAS HAROLD
IPC: H04Q3/42
Filed: 1948-09-30
Abstract: 667,370. Automatic exchange systems. POSTMASTER GENERAL. Sept. 1, 1949 [Sept. 30, 1948], No. 25523/48. Class 40 (iv). In a register-controller system if the register-controller fails to complete the connection due for example to an all-trunks-busy condition, or to the seizure of a faulty trunk at a point ahead, the partial connection is released, the trunk to which the calling line and the register-controller are connected is changed, and the registercontroller makes another attempt to set up the connection over the second trunk. A calling line 1, 2 (Fig. 1), may be connected by uniselector line-finders to one of a number of trunks, each line-finder being associated with a particular trunk. Only the two line-finders comprising banks W11, W12 ... W16 and banks W21, W22 ... W26 which are associated with trunks TR1 and TR2 respectively are shown. Relay L pulls up to the calling loop in the usual way, marks the calling line in the line-finder banks, and extends ground to a trunk marker TM which marks a free trunk which is the next to be used, in this case TR1. The ground is extended over bank TM1 to operate relay 1ST and latch-magnet 1LM of trunk TR1. Relays 1CD and 1B are thus connected to wiper W14 of the associated line-finder which rotates its wipers in search of the marked line. Highspeed relay 1CD pulls up to stop the finder and 1B follows at leisure. The latter relay brings up the calling line relay H, and extends ground over bank TM2 to the driving magnet MDM which self-drives until its wipers reach a free trunk. Relay 1ST falls away and disconnects 1CD and 1B, of which 1CD releases immediately but 1B being slow to release remains up until held by the operation of 1A which results from that of H. Relay G operates and remains up while the trunk marker uniselector wipers are rotating to prevent any trunk from being marked during this period. The trunks are connected to register-controllers over trunk-finders of which a pair is provided for each register-controller. Thus a registercontroller R (Fig. 2)-only part of which is shown-is connected to a first trunk-finder (banks WR1 to WR6) and to a second trunkfinder (banks WT1 to WT6). In addition to the usual multipling of the banks of all first and all second trunk-finders serving the same group of register-controllers, the banks WR4, WR5 and WR6 of all the first trunk-finders are respectively multipled to the banks WT3, WT4 and WT5 of all the second trunk-finders. A register-marker RM, similar to the trunk marker TM, allots free register-controllers in turn. The operation of relay 1A also brings up ILR (Fig. 1), which marks the calling trunk TR1 in the banks WR2 of the first trunkfinders and extends ground over bank RM1 of the register-marker to operate relay RST and latch-magnet RLM1 in the marked registercontroller. When the first trunk-finder reaches the marked trunk RCD pulls up over bank WR2 to stop the finder, and RB follows. The register-marker steps on to a free registercontroller releasing RST and RCD, relay RG preventing marking during stepping. The operation of RB extends ground over bank WR3 to bring up 1H which releases 1LR and extends ground from front 1A over bank WR4 to operate RA which then holds RB. Dialling impulses incoming from the calling line are repeated by 1A in the trunk to RA which controls the registers (not shown) in known manner. The register-controller in turn controls the exchange switches according to the system in use. As shown in the drawing the register-controller leads OG1 and OG2 are connected over back contacts of 1X in the trunk to the outgoing speaking wires and over this circuit dial pulses are transmitted to set the switches. In the normal case the registercontroller sets up the connection and sends a release signal (by means not shown) to the trunk, causing 1B to release and IX to operate, Relay 1A falls away and the register-controller is released. Connection not set up. The fact that the connection has not been completed can be detected by means not shown in the registercontroller (e.g. the absence of the supervisory tone which normally signals success) and this is assumed to result in the operation of TF in the register-controller, whereupon the second trunk-finder is started up and relay 1T in trunk TR1 operates over bank WR1. Relay 1T brings up 1TA, marks trunk TR1 in bank W16, and extends ground to the transfer trunk marker TTM individual to the group of trunks served by the same line-finder group and the same trunk-finder group. Bank TTM1 is multipled to bank TM2 of the trunk marker so that the transfer trunk marker is prevented from marking busy trunks. The ground is extended over bank TTM2 to operate the TR relay in a free trunk, e.g. trunk TR2 (Fig. 1). Relay 2TR therefore operates, brings up 2TS, energizes the latch-magnet 2LM to start the associated line-finder, and connects 2CD and 2B to wiper W25. When the line-finder wipers reach the contact marked by 1T over bank W16 relay 2CD pulls up to stop the finder, and 2B follows to connect 2A to the calling line. The resulting operation of 2A cannot bring up 2LR in the normal way since 2TS is up, but 2LT (operated by 2TS) marks the trunk TR2 in bank WT1 so that when the second trunkfinder reaches the trunk TR2 it is stopped by the operation of TCD, which also brings up 2H and 2HT over bank WT2. Relay 2HT releases 2LT and extends ground over bank WT6 to operate RT in the register-controller provided 2B is up. The operation of RT releases TF, 1T and 1H (whereupon 1B, 1A and 1TA fall away and the first trunk TR1 is released) and signals the register-controller that the second attempt to set up the connection over a second trunk may be commenced.